Is this, longish rtw route, award legal?

I'm looking to go to BKK in Christmas - low and behold, I've found a way!
I thought I was too late. Anyway, here it is

NYC-IAD-LHR day flight (only one I could fund but happy to change to direct and overnight) UA J

This would require an overnight - is that legal?

LHR-BKK TG First

STOP

BKK-TPE short layover

TPE-JFK

I'm thinking there are two things that may be a hurdle - one, the overnight in LHR, which I think is justified as there are no other J options, and two, the fact that it's RTW.

Is this possible? Or only if I have a really friendly agent?
Thanks!